JPH07122938A - Ssb modulation circuit and ssb demodulation circuit - Google Patents

Abstract

PURPOSE:To eliminate only the sum component of SSB signals and to easily vary carrier wave signals by changing the cut-off frequency of a low-pass filter by the control signals of a signal generation circuit. CONSTITUTION:Input signals are impressed through an input terminal 1 to phase shifters 2 and 3 and phase-shifted in the respective phase shifters. The output signals of the phase shifters 2 and 3 are respectively impressed to modulators 4 and 5 and the carrier wave signals are respectively modulated. Thereafter, the output signals of the modulators 4 and 5 are added in an adder 6 and the difference component of the input signals and the carrier wave signals and the sum component which was not eliminated are generated from the adder 6. Further, the output signals of the adder 6 are impressed to the LPF 7 and the sum component of the output signals is attenuated. Thus, the SSB signals of only the difference component of the input signals and the carrier wave signals are generated from an output terminal 8. In the meantime, reference signals impressed through the input terminal 9 are frequency-divided by a frequency dividing number N in a frequency divider 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SSB modulating circuit and an SSB demodulating adjusting circuit used in a secret communication circuit of a cordless telephone.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional circuit. (1) is an input terminal to which the input signal f _s is applied, (2) and (3) are phase shifters, (4) and (5) are modulators, (6) is an adder,
(7) is a low-pass filter, (8) is an output terminal, (9)
Is an input terminal to which the reference signal f _r is applied, (10) is a frequency divider, and (11) supplies two carrier wave signals f _c having a 90-degree phase difference to each other to the modulators (4) and (5). It is a carrier wave generation circuit.

The input signal f _s is applied to the phase shifters (2) and (3) via the input terminal (1), and the phase of the input signal f _s is shifted. The phase difference between the output signals generated from the phase shifters (2) and (3) is π / 2. On the other hand, the reference signal f
_r is applied to the frequency divider (10) via the input terminal (9) and is frequency-divided. After that, the output signal of the frequency divider (10) is applied to the carrier wave generation circuit (11), and based on the output signal, the first carrier wave signal f _c and the first carrier wave signal out of phase with π / 2. 2 the carrier signal f _c 'is generated in the modulator (4) and (5) respectively.

In the modulator (4), the output signal of the phase shifter (2) modulates the first carrier signal, and the difference component (f _s -f _c ) between the input signal f _s and the carrier signal f _c and the sum thereof. Component (f _s + f
DSB (Double Side Ban) including _c )
d) Generate a signal. Further, the modulator (5) modulates the output signal of the phase shifter (3) and the second carrier signal. Further, the DSB signals generated from the modulators (4) and (5) are added in the adder (6), and the SSB of only the difference component (f _{s to} f _c ) between the input signal f _s and the carrier signal f _c is added. (S
single side band) signal is added by adder (6)
Arises from.

However, since the phase shift amount of the phase shifter generally changes with respect to the frequency of the input signal, the phase difference between the output signals of the phase shifters (2) and (3) is relative to all frequencies. Does not reach π / 2. In this case, the adder (6) as well as the difference component of the input signal f _s and the carrier signal f _c (f _s ~f _c) from the sum component (f _s + f _c) is also generated. Therefore, LPF
By inserting (low pass filter) (7),
The sum component (f _s + f _c ) is sufficiently attenuated in the LPF (7) so that the SSB signal having only the difference component is generated from the output terminal (8).

[0006]

By the way, the SS shown in FIG.
In the B modulation circuit, the frequency band of the difference component and the sum component of the SSB signal generated from the adder (6) is changed by changing the frequency of the carrier signal generated from the carrier generation circuit (11). Therefore, in order to generate only the difference component from the output terminal (8), it is necessary to change the cutoff frequency of the LPF (7) according to the frequency of the carrier signal so that only the sum component is attenuated. Generally, LPF
When changing the cutoff frequency of (7), the variable element (for example, a resistor or a capacitor) forming the LPF (7) is changed to adjust the cutoff frequency of the LPF (7). Therefore, it is not easy to frequently adjust the cutoff frequency of the LPF (7) according to the frequency of the carrier signal.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points, and is an SSB modulation circuit having a phase shifter for generating a first signal and a second signal having a 90-degree phase from each other from an input signal. A first modulator for modulating the output signal of the first phase shifter, and a second modulator for modulating the output signal of the second phase shifter
Modulator, adder for adding output signals of the first and second modulators, low-pass filter for passing output of the adder, first and second modulated signals of the first and second modulators And a signal generation circuit for generating a control signal for varying the cutoff frequency of the low-pass filter.

Further, the signal generating circuit compares the phase of a reference signal generating circuit for generating a reference signal, a filter for passing the reference signal, a phase of the reference signal and an output signal of the filter, and responds to the comparison difference. And a phase comparator for controlling the filter is provided. Furthermore, in an SSB demodulation circuit having a phase shifter that creates first and second signals having a 90-degree phase with each other from an input signal, a first modulator that modulates an output signal of the first phase shifter and a second modulator A second modulator that modulates the output signal of the phase shifter, an adder that adds the output signals of the first and second modulators, a low-pass filter that passes the output of the adder, and the first and first A signal generation circuit for generating first and second demodulated signals of the two modulators and a control signal for varying the cutoff frequency of the low pass filter is provided.

[0009]

According to the present invention, in the first modulator, the two output signals generated by the phase shifter and having 90 ° phase with each other modulate the first and second modulated signals generated by the signal generating circuit, respectively. The modulated signals are added by the adder, and then the signal that has passed through the low pass filter is generated as an output signal. Further, the cut-off frequency of the low-pass filter is changed by the control signal of the signal generating circuit, so that the signal passing through the low-pass filter is changed.

In the signal generation circuit, the output signal of the frequency divider generated by dividing the reference signal is passed through the filter, and then the phase comparator compares the output signals of the frequency divider and the filter. Then, the filter is controlled according to the comparison difference. The output of the frequency divider is generated as the first modulated signal, the output of the filter is generated as the second modulated signal, and the input signal of the filter is generated as the control signal.

[0011]

FIG. 1 is a diagram showing an embodiment of the present invention,
(12) is a phase comparator, (13) is a loop filter,
(14) is an amplifier, and (15) is a filter in which the amount of phase shift of the input signal changes according to the output signal of the amplifier (14). Note that, in FIG. 1, the same circuits as those in FIG.

The input signal f _s is applied to the phase shifters (2) and (3) via the input terminal (1) and is phase-shifted in each. The output signals of phase shifters (2) and (3) are applied to modulators (4) and (5), respectively, and carrier signal f _c
Respectively. Then modulators (4) and (5)
Output signals are added by the adder (6), the input signal f _s and the difference component of the carrier signal f _c (f _s ~f _c) and removed has not been sum component (f _s + f _c) an adder ( It occurs from 6).
Further, the output signal of the adder (6) is applied to the LPF (7), and the sum component of the output signal is attenuated. Therefore, the SSB signal having only the difference component between the input signal f _s and the carrier signal f _c is generated from the output terminal (8).

On the other hand, the reference signal applied via the input terminal (9) is divided by the frequency division number N in the frequency divider (10). The output signal of the frequency divider (10) is filtered by the filter (1
5) and the phase comparator (12) and also as a carrier signal f _c to the modulator (4). The output signal applied to the filter (15) is
After the phase is shifted by 5), it is applied to the phase comparator (12). In the phase comparator (12), the frequency divider (1
0) and the output signal of the filter (15) are compared in phase, and a signal corresponding to the phase difference is generated. Phase comparator (1
The signal generated from 2) is smoothed by the loop filter (13), further amplified by the amplifier (14), and applied to the filter (15) as a control signal. The characteristics of the filter (15) change according to the control signal, and the phase of the output signal of the frequency divider (10) applied to the filter (15) changes.

When the phase difference between the output signals of the frequency divider (10) and the filter (15) becomes π / 2, the phase comparator (1
2), the loop consisting of the loop filter (13), the amplifier (14) and the filter (15) is locked and a first control signal is applied to the filter (15). The first control signal is also applied to the LPF (7),
Since (7) has a configuration in which the cutoff frequency is variable by the control signal, the LPF (7) is generated by the first control signal.
Is set to the first cutoff frequency.

As described above, the output signal of the frequency divider (10) is applied to the modulator (4) as the carrier signal f _c , and the output signal of the filter (15) is also the carrier signal f _c.
And the carrier signal f _c ′ whose phase is shifted by π / 2 is the modulator (5)
Applied to. Thus, in the modulator (4) and (5), respectively, an input signal f _s is the output signal of the divider (10), also the phase and [pi / 2 shift input signal f _s of the input signal f _s' is The output signal of the filter (15) is modulated.
When the loop is in the locked state, the frequency divider (10)
Since the phases of the output signals of the filter and the filter (15) are shifted by π / 2, they can be used as the carrier signal of the SSB modulator.

Here, consider the case where the frequency of the carrier signal is changed by changing the frequency division number of the frequency divider (10).
When the frequency division number of the frequency divider (10) is set small and the frequencies of the carrier wave signals f _c and f _c ′ become large, the input signal f _s generated from the adder (6) and the carrier wave signal f _c are The frequency band of the sum component becomes large. Further, the loop includes the frequency divider (1
0) output signal is locked and the amplifier (1
The second control signal is generated from 4). The second control signal is LP
Applied to F (7), the cutoff frequency of LPF (7) is the first
It becomes large based on the control signal. Therefore, the sum component applied to the LPF (7) is sufficiently attenuated.

On the contrary, the frequency division number of the frequency divider (10) is increased,
If the frequency of the carrier signal f _c and f _c 'is small, the frequency band of the sum components generated from the adder (6) becomes small.
In addition, the third control signal is generated from the amplifier (14), and the LP
The cutoff frequency of F (7) becomes small based on the third control signal. Therefore, the frequency band of the sum component (f _s + f _c ) of the input signal f _s and the carrier signal f _c generated from the adder (6) changes as the frequency of the carrier signal changes, but the LPF changes accordingly. Since the cutoff frequency of (7) also changes, the sum component is sufficiently attenuated by the LPF (7).

FIG. 3 shows a concrete example of the configuration of the LPF (7) shown in FIG.
Is. The LPF of FIG. 3 is the same as the conventional one.
The description of the configuration and the operation will be omitted. LP of Figure 3
The cut-off frequency f of F is the differential amplifier (16) and (17).
The transconductance of gm ₁And gm₂,condenser
The capacitance of (18) is C, and the transistors (19) and (2
0) The emitter resistance of r_eThen,

[0019]

[Equation 1] Also, the transconductance gm ₂ of the differential amplifier (17)
Is proportional to the current I ₂ of the constant current source (21), the cut-off frequency f is proportional to the current I ₂ . Furthermore, a constant current source (1
The current of 8) is changed by the control signal generated from the amplifier (14) of FIG. Therefore, the cutoff frequency f of the LPF of FIG. 3 can be changed by the control signal.

In the circuit of FIG. 1, a modulation signal is applied as an input signal and a demodulation carrier signal is applied to the modulators (4) and (5), and the same operation as that of FIG. 1 is performed. When operated, it can be used as an SSB demodulation circuit.

[0021]

According to the present invention, when the frequency of the carrier signal changes, the cut-off frequency of the LPF (7) also automatically changes accordingly. Therefore, even if the frequency of the carrier signal is changed, the adder is always used. Only the sum component of the SSB signal that has not been removed can be removed. Therefore, it is possible to change the frequency of the carrier signal easily and frequently. Furthermore, since it is not necessary to change the cutoff frequency of the LPF (7) by using a variable element, the SSB modulation circuit of the present invention is an IC
It is suitable for

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

FIG. 3 is a circuit diagram showing a specific configuration example of a low pass filter (7) in FIG.

[Explanation of symbols]

 1 Input Terminal 6 Adder 8 Output Terminal 11 Carrier Wave Generation Circuit 14 Amplifier

Claims (3)

[Claims] 1. An SSB modulation circuit having a phase shifter for generating first and second signals having a 90-degree phase with each other from an input signal, the first modulator modulating an output signal of the first phase shifter, A second modulator that modulates the output signal of the second phase shifter; an adder that adds the output signals of the first and second modulators; a low-pass filter that passes the output of the adder; An SS including first and second modulation signals of first and second modulators and a signal generation circuit for generating a control signal for varying a cutoff frequency of the low-pass filter.
B modulation circuit. 2. The signal generating circuit compares a reference signal generating circuit that generates a reference signal, a filter that passes the reference signal, a phase comparison between the reference signal and an output signal of the filter, and determines a comparison difference. And a phase comparator for controlling the filter, wherein the first carrier signal is an output signal of the frequency divider, the second carrier signal is an output signal of the filter, and the control signal is an input signal of the filter. The SSB modulation circuit according to claim 1, wherein 3. An SSB demodulation circuit having a phase shifter for generating first and second signals having a 90-degree phase with each other from an input signal, the first modulator modulating an output signal of the first phase shifter, A second modulator that modulates the output signal of the second phase shifter; an adder that adds the output signals of the first and second modulators; a low-pass filter that passes the output of the adder; An SS including first and second demodulated signals of first and second modulators and a signal generation circuit for generating a control signal for varying a cutoff frequency of the low-pass filter.
B demodulation circuit.